Stocks and the US dollar began surging in September after Japan's central bank sliced its key interest rate in half to a record-low 0.5 percent.

In recent years, the plunge in the dollar's value against the yen - from the annual average of 144.79 yen in 1990 to the 80-yen level in April - has hurt Japan's export-oriented economy by making its products more expensive in other currencies.

The cut in September put Japan's official discount rate far below those in other leading industrialized nations, including the Federal Reserve's 5.25 percent rate in the United States.

In the last six days, the Nikkei index has risen 871.27 points, or 4.55 percent.